Had a look at the Gherkin, looks like it has a PCB plate option but it still uses the PCB for the switches which would make it more rigid. Can't find the Cartel board on their site or the first page of GBs here so
Very interesting about thermal expansion, could be a big problem depending where you live and how cool you like your workspace. Out of interest what switches were you using? If the switches also shrank it might not be a problem. Or maybe it would be worse...
Here's the Cartel Contra:
https://cartel.ltd/projects/contra/RE: my board/thermal expansion - I seems I wasn't clear in my description. The switches and switch plate are fine (aluminium combined chassis and switch plate, regular PCB), the issue, and it's not a huge one, is the top acrylic cover (the shiney visual bit) which was cut with keycap clearances a little too tight. At normal room temperature the caps pass through the opening in the acrylic top fine, but on a cold day with no heating I get a little binding between the
keycap and cover plate in the bottom left
- and top right [backspace] of the board.
Based on the above I'm extrapolating to the concept of using acrylic for a switch plate over a PCB. Based on quick numbers, a 20degC change causes a 0.75mm expansion in my 500mm board for acrylic. It's probably not a big deal for a small board which doesn't see a big temperature swing, but my board is big and office heating inconsistent so I notice this effect for a couple hours in the morning. In comparison Alu would expand 0.25mm, stainless steel 0.2mm-ish over this temp range and material length, which is a much more forgiving number for a mounting plate/expansion compatibility.
[Links in my sig for images of the build just in case]